计及AC-UHVDC系统无功补偿和谐波特性的UHVDC交流滤波器可靠性建模

Reliability Modeling of AC Filter in UHVDC Considering Reactive Power Compensation and Harmonic Performance Evaluation of AC-UHVDC System

特高压直流输电(ultra high voltage direct current,UHVDC)故障对电网影响严重,建立精确的可靠性模型十分必要。交流滤波器(ACfilter,ACF)子系统与交流母线并联,可补偿无功,减少谐波。谐波过大或无功不足均可能导致UHVDC降额。提出一种计及无功补偿和谐波特性的ACF可靠性模型,用矩阵组合将单一型号滤波器状态空间(state space,SS)合并成ACF所有配置方案的SS模型。由ACUHVDC基波潮流确定ACF需提供无功容量等级,进而将配置方案分组。由谐波潮流计算各配置方案的谐波指标,若谐波电流超标,将配置方案移至容量等级较低分组。根据分组情况,合并配置方案为五状态容量模型。算例表明,配置方案按无功补偿分组后,可能会因不满足滤波指标而被移至0%CL分组,故0%CL状态概率可能比75%CL、50%CL或25%CL状态高。

Due to the large transmission capacity of the ultra high-voltage direct-current(UHVDC), its failure affects the connected AC grids. Therefore, it is important to establish an accurate reliability model of the UHVDC line. The AC filter(ACF) subsystem, which is parallel to the AC bus, helps to compensate the reactive power consumed by the converters and absorb the harmonics flowing into the AC grids. The overlarge harmonic current can reduce the transmitted power, so does the insufficient reactive power. In this paper, the reliability model of the ACF subsystem was newly proposed by considering reactive power compensation and harmonic performance evaluation. The state space(SS) models of the filters were built by their types respectively and combined by the transfer rate matrix to obtain the transfer rates among the states of the configuration schemes of the ACF, i.e. the types and numbers of the available filters. The fundamental power flow model of the AC-UHVDC system was built to quantify the compensated reactive power, by which the configuration schemes of the ACF were grouped. The harmonic power flow model was utilized to evaluate the harmonic performance. The configuration schemes which do not meet the harmonic standards were removed to the groups with lower capacity level. Then the SS model of the ACF configuration schemes were aggregated to 5 states. The numerical analysis demonstrates that the probability of 0% CL may be higher than those of 75% CL, 50% CL, and 25% CL. It is because that many configuration schemes in those CL groups dissatisfying the harmonic standards are removed to the group of 0% CL.